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Aquarium Fish

How to keep discus fish?

How to keep discus fish?

If you are reading this you may have thought about keeping discus fish before. No wonder these fish look amazing and bring a special flair to the aquarium with their appearance. With this article, we would like to make it easier for you to get started in the world of discus. Then let's start!

The discus (Symphysodon) is one of the few aquarium fish for which the origin is one of the most critical factors for keeping. In South America, this is the Amazon basin, the most extensive water system in the world, with a catchment area of almost 7.2 million km², equivalent to two-thirds of the size of Europe. It stretches from the Peruvian Andes to the Atlantic Ocean. Consisting of about 15,000 rivers, it spans seven countries and provides 20-25% of the world's fresh water. This information is important because this area contains many freshwater species, from blackwater swamps to karst rivers to crystal clear rivers. Discus fish occur throughout the range of this highly diverse habitat. Because wild-caught specimens come from various locations and water parameters, their perfect keeping varies from bloodline to bloodline. The range of water hardness and pH that discus populations are found in their natural habitat is broad. However, water parameters most ideal for a particular population are those in their native habitat. Therefore, the maintenance of some bloodlines from the discus culture can vary greatly (e.g., S. aequifasciatus, which in most cases thrives best between pH 6.5 and 7 and pH 5-12°dH, while an S. discus requires pH 5-5.5 and °dH close to 0). Therefore, the information below generalizes the ideal housing conditions for discus fish, which may vary depending on the species and bloodline. It is worthwhile to research the natural habitat of the discus and create an environment as similar as possible. Currently, there are four species of the genus Symphysodon: the Common Discus (S. aequifasciatus), the Brown Discus (S. haraldi), the Heckel's Discus (S. discus), and the Green Discus (S. tarzoo.). The most common species in Hungary today is Symphysodon aequifasciatus, the easiest to keep. In some descriptions, S. aequifasciatus and S. haraldi are described as the same species, although they differ in keeping and habitat.

Discus Fish

Common discus (S. aequifasciatus)

Generally, a medium-sized (17-22 cm) species prefer harder, colder, more alkaline water than other discus. It is found in central Amazonia and areas west of Solimőes.

Brown discus (S. haraldi)

Generally (for discus), a species (18-20 cm) that prefers moderately acidic water, i.e., soft water and medium temperatures. Native to eastern Amazonia and the lower reaches of the Amazon River.

Heckel's Discus (S. discus)

This discus species generally has a large body (20-25 cm) and prefers very soft, warm, highly acidic water. It is found in the rivers Rio Negro, Uatuma, Nhamunda, Tombetas, Abacaxis, and the surrounding swamps.

Green Discus (S. tarzoo)

Usually, a smaller species (13-17 cm) prefers more acidic, softer, and moderately warm water (compared to other discus). Native to the Nanay River and associated swamps in the western Amazon.

Discus Fish

Keeping discus fish only in soft water

Aquarium parameters:

  • Minimum 200L (recommended >500)
  • Water column height minimum 50-60 cm
  • Ideal lighting: low/medium brightness 8-12 hours/day

Water parameters:

  • Temperature: 28-30°C
  • Water hardness: 0-4° dH
  • pH: 5-6.5
  • Water load 50-60l per adult specimen
  • Peaty water

Fish characteristics:

  • Swarm fish, at least 6-8 fish should be kept in >500 liters
  • Life expectancy: 10-15 years
  • They are peaceful, but since they are perches, they regularly fight among themselves
  • They are omnivores, and for beautiful, healthy fish in good condition, feeding them with 80-90% live or frozen food is recommended. If they are raised on dry food only, they can become sickly.
  • They usually stay in the lower 2/3 of the aquarium.

Preparing the aquarium:

Soft water has a very low dissolved mineral content, so an aquarium filled only with pure RO water or distilled water is unsuitable for fish. The best way to get good soft water for the discus aquarium is to salinate the water produced with RO with a unique remineralizer. It should be noted that the salt mixture contains many minerals, not only minerals that cause the water's hardness, and that the water, after treatment, must have at least 3°dH. For water below 3°dH, mixed bed ion exchange resins can be used. This method is much more complicated and expensive than using RO water. But essential minerals which don't cause water hardness remain in the water.

Check your water parameters regularly if you choose to use the mixed bed resin method. The check concerns the KH-GH ratio and all other dissolved chemicals that accumulate in the water due to the aquarium decoration you use or the operation of your aquarium. Nowadays, we don't need a separate laboratory for this because we can quickly check any water parameter with the easy-to-use water tests available on the market.

Choosing a substrate:

Young specimens may be sensitive to decomposition residues that accumulate in the substrate. Therefore, it is advisable to keep them without a substrate (in which case the bare bottom of the aquarium should not reflect). Or in a very thin layer (1-2 cm) of a fine-grained easy-to-clean substrate (e.g., Dennerle Quartz gravel) that does not affect the water parameters. This precaution is not necessary from the age of about two years if they are kept in a suitable environment. They can even be kept in active soil.

Discus fish do not like strong water currents. They, therefore, do not feel comfortable in planted high-tech aquariums with external high-performance filters, which are required to maintain such aquariums. The filter's flow rate should be at least 3 to 4 times the net volume of the aquarium. Try to break the flow at the filter inlet as much as possible, for example, using a Lily pipe, a Poppy type glass outflow, or a Spin pipe. The best solution is to choose a filter device with a large filtration capacity and an adjustable flow rate.

In soft water systems, plant nutrition can easily disturb the microbiological balance of the water. Therefore, it is better to use slow-growing plants such as epiphytes (e.g., Microsorum or Anubias) that can find sufficient nutrients in a functioning aquarium.

If your aquarium has a suitable substrate, you can also keep heat-tolerant plants (e.g., Vallisneria), which absorb nutrients mainly through their roots. Nutrient capsules for the substrate can be used in fine-grained substrate, as they do not affect the microbiological balance of our water if they remain in the soil.

One should pay attention to the fact that the commercially available specimens are acclimatized. This means that they hatch in the above water parameters, but during their rearing, the breeder gradually hardens and alkalizes the water to facilitate their subsequent care. The fish must therefore be acclimatized to the new parameters, which can be done, among other things, as follows:

  • Try to buy specimens as young as possible (<5cm). Put them in a quarantine tank (approx. 100l) with the water parameters of the "source water," and replace 10% of the water in the quarantine tank with the water of the future aquarium every day. This way, you will get almost the same parameters in both aquariums in 2 weeks, and then you can safely transfer the fish.
  • Another method is putting the fish in a tank containing about 30 liters of water. Then the "future" water is slowly fed into the aquarium through a thin hose. That way, the aquarium is filled in about 8 hours. When using this method, make sure that the aquarium is not overpopulated during the acclimation period. Do not put more than 3 to 4 discus fish in a 30-liter aquarium at one time. Once the aquarium is filled up, the discus can be moved. It is important to note that this should only be done with juveniles. Adult discus fish do not always survive a significant and sudden change in the water parameters.

Discus Fish

Keeping discus in softened tap water

Water parameters:

  • pH: 6-7
  • Water hardness: 8-15°dH

Fish characteristics:

  • Size: 15-17cm
  • Life span: 6-8 years

These are the most commonly chosen water parameters of discus keeping. The best and easiest way to get suitable water parameters for water produced by an RO system is to re-salt it with remineralization salt. In this way, the RO water gets only the minerals we add. In many places, tap water can also meet these levels, which can be a good choice. But unfiltered tap water can contain many substances harmful to livestock (e.g., heavy metals, chlorine). A water conditioner should be used to neutralize harmful substances in the tap water.

You can keep any heat-tolerant plants in it, and the water values will not tip with proper aquarium maintenance.

Purchased fish can be immediately placed in the aquarium after the usual acclimation measures. However, adult fish are somewhat smaller, and their life span is shorter (6-8 years). Some breeders have acclimated their discus fish so well that they spawn under their adapted water parameters. But hatchlings, larger specimens, or a longer life span are rare.

All other characteristics of the discus are the same as when breeding in "soft water."

Discus Fish


Light your aquarium for a relatively long period with low light intensity (8-12 hours per day). It is also good to have a night light, which should be a very low-intensity moonlight. You should not be able to see details in the aquarium due to the night light being turned on! Many moonlight lightings on sale are way too bright. The night light should be programmed to run 30 minutes after the main light is turned off and 30 minutes before the main light is turned on.

Night light helps discus fish orient themselves by creating a transition between daylight and darkness at night, thus relieving stress. Night lights should not be on all night because fish do not have eyelids and only sleep in the dark. Therefore, they should be in the dark for 7-8 hours per night. It is essential to point out that while a sunrise simulation mode of aquarium lighting is perfect for fish, and should be used as a transition to night lights. However, the main aquarium lighting set at the lowest level should not replace a night light.


Discus fish are cradle-mouth bass; although they are omnivorous, they mainly eat lower crustaceans and worms. If fed incorrectly, they can become nutrient deficient, quickly become ill, and become victims of irreversible deficiency diseases such as cephalopenia. The nutritional value of freeze-dried food (e.g., dried Tubifex) is low, and feeding it should be avoided. Feed mainly live or frozen foods. Nevertheless, do not exclude high-quality dry food specifically for discus fish, but do not make this the complete food. If you feed your fish a varied diet, they will likely be very healthy.

Oxygen (O2) supply, gas exchange

The solubility of oxygen (O2) in water decreases with increasing temperature. For physical reasons, warm water can absorb less oxygen and has a lower oxygen-holding capacity than cold water. This means that at a water temperature of 30°C, no more than approx. 7.5 mg/l oxygen can be dissolved in the water. In comparison, water with a temperature of 20°C can hold about 9.0 mg/l of O2. Additional aeration via an air pump and bubble stone can be dispensed in most cases. The most important thing is the filtration or, respectively, that through the filter outlet, constant gas exchange is ensured by sufficient water surface movement. Oxygen content of less than 3.0 mg/l represents a life-threatening value for the livestock. If you feel unsure about the O2 value in your aquarium do frequent O2 water testing. In case of a highly reduced O2 level, the best first aid is a large water change of min. 50%.

Choosing healthy fish

It is worth choosing a species that is easy to keep at first (e.g., S. aequifasciatus). When purchasing, ask about the requirements regarding the bloodline of the specimen. When selecting fish, make sure you are purchasing healthy specimens. The following may be warning signs, among others:

  • A fuzzy spot in the pectoral and caudal fins indicates a fish with nutrient deficiencies.
  • A distended or sunken abdomen, which may indicate intestinal inflammation or worms
  • Permanently closed fins, indicating the presence of parasites
  • A disproportionately large eye or elongated body shape indicating that the fish is underdeveloped

What other fish can be kept with discus?

Discus fish have precise water requirements. So if you choose other fish that are kept the same way as discus fish, you have already narrowed down the choices. You could select a heat-tolerant Corydoras (e.g., Corydoras sterbai), a quiet or more sedate swarm fish (e.g., Red, Green neon, or Petitella), an algae eater such as Ancistrust, or perhaps a Dwarf cichlid (e.g., Microgeophagus, Apistogramma species).

Additional thoughts

Discus fish are susceptible to poor water quality, so the water should be kept as clean and stable as possible. This can be achieved by the following methods, among others:

  • Regular, significant water changes, at least 50% of the aquarium water, at least once a week. Clean the aquarium simultaneously as the water change, for example, by removing mulm on the substrate.
  • By chemical filtration: operate a filtration system with filter media that filters out nitrite, nitrate, and ammonia (e.g., with Seachem Purigen or activated carbon).
  • Keeping discus fish together with Angelfish is not recommended, as Angelfish are intermediate hosts of certain parasitic diseases. The parasites do not make the Angelfish sick, but they can be fatal to the discus (not all Angelfish are infected with parasites, but it isn't easy to find out).
  • They should not be kept with very fidgety fish (e.g., Danios), as their "fidgety" behavior causes stress to the discus.

Discus fish kept in the same tank should always come from the same source. This is because discus are particularly sensitive to the microbiological balance. It may vary slightly from culture to culture. If discus fish from different habitats with different microbiological environments are kept together, then the microbial balance of the swarm will be disturbed. That, in turn, can lead to immune deficiencies and possible disease. This phenomenon usually manifests as cancer, swim rot, or fish mold. These diseases can be treated, but they may also lead to the death of the fish. If the appropriate knowledge is missing, it can result in an uncontrollable wave of infection.

Discus fish are particularly susceptible to intestinal infections, intestinal worms, and parasites. It is advisable to occasionally feed them food containing garlic, add garlic extract to their food, or treat them with a worm drug.

Higher water temperatures of 28-30 degrees are essential for proper discus fish keeping. Make sure your thermostatic heater maintains this temperature when the surroundings are colder. 

Gender identification and breeding

In principle, there is no difference between male and female discus fish, and their ovariole can determine their gender during spawning. However, in some bloodlines, breeders have selected breeding pairs where the male has a characteristic fin lesion compared to the female for many years. In these bloodlines, the elongation of the dorsal fin or the shape of the caudal fin is an indicator that the individual belongs to the livebearers. Experienced discus keepers can often determine a fish's sex from its behavior.

Breeding pairs

Discus fish, like most cradlemouth bass, are pair-breeding fish. Sometimes pairs can breed at a younger age (5-6 cm). Pairs can be recognized as they often separate and do everything together. They are sexually mature at 12 months old, but the first successful spawning is not expected until they are about 18 months old.

The breeding aquarium

Aquarium of at least 125 liters, preferably with a sponge filter. Preferably with a sponge filter. No substrate and no decorations, with a spawning cone in the center.

The water

The water can vary considerably from species to species. Still, in general, water similar to the water parameters of a soft water aquarium, preferably acidified with tannic acid at the minimum values (0°dH, pH 5,5-5,8, 28-29°C), is required. It should be noted that a culture medium of over 1000 liters, 0°dH and a pH of 4.5-4.8 for S. discus does not always lead to success. Success can be achieved with a pH of 6-7, a water hardness of over 5°dH, and a culture medium of around 100 liters for S. aequifasciatus.

Spawn and fry

The pair first occupies a flat area for themselves, on which they later lay 150-200 eggs, which are guarded jointly by the male and female. The fry hatch within 52-54 hours. The fry, which aren't yet able to swim, are transferred by the parent pair. After 4-5 days, the fry can swim. During the first two weeks, they only consume secretions produced by the parents. Later, they can be fed with freshly hatched Artemia. The fry will only accept live food until they are two months old. After, they can be acclimated to frozen or dry food.

Keeping discus fish is not easy, so it is recommended to beginners only after a serious study. The discus fish are definitely worth considering for those with an aquarium of more than 300 liters or who want to acquire one. The extraordinary shape, colors, and patterns of the discus fish and the fry breeding can be an unforgettable experience for any aquarist.

Still unsure of how to keep Discus fish?

If you have any questions about keeping a discus, our customer service will be happy to help.

Author/source: Borók János

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